IBM PC Emulator

An IBM PC Emulator written in C using SDL3

Emulated Hardware

i8086 CPU
i8237 DMA
i8253 PIT
i8255 PPI
i8259 PIC
i8272 FDC (NEC uPD765)
MDA ISA Card (IBM Monochrome Display Adapter)
CGA ISA Card (IBM Color Graphics Adapter)

Building

The project is built in Visual Studio 2022

Dependencies
I8086	https://github.com/tommojphillips/i8086
SDL3 3.2.24	https://github.com/libsdl-org/SDL
SDL3_ttf-3.2.2	https://github.com/libsdl-org/SDL_ttf
ImGui 1.92.3	https://github.com/ocornut/imgui/tree/v1.92.3

Clone the repo and submodules

git clone --recurse-submodules https://github.com/tommojphillips/ibm_pc.git

cd dir to ibm_pc

cd ibm_pc

Fetch SDL3/SDL3_TTF VC Release

scripts\fetch_sdl3.sh

Open lib\UI\vc\UI.sln, build
Open vc\ibm_pc.sln, build, run.

Make sure these files are next to ibm_pc.exe or on your PATH:

SDL3.dll
SDL3_ttf.dll
UI.dll

If building from source, and launching through visual studio, all .dll files are already on your PATH. You only need to copy the .FON files to the same directory as ibm_pc.exe

FONT Files

Font files are required for full functionality. FONTS can be found here: https://int10h.org/oldschool-pc-fonts/download/

Description	File
MDA Font 9x14	Bm437_IBM_MDA.FON
CGA Font 8x8	Bm437_IBM_CGA.FON

They have been included in the fonts\ directory of the repo.

ROM Files

Some ROMS are required for full functionality. ROMS can be found on 86Box's github: https://github.com/86Box/roms/

IBM PC 5150 ROM

The earlier 1981 BIOSes only read the first 4 bits of SW2 resulting in a max of 544KB of RAM
The later 1982 BIOSes read the first 5 bits of SW2 resulting in a offical max of 640KB of RAM

Description	Date	Size	Address	Location
IBM 5150 U33	24 APR 1981	8K	0xFE000	`machines\ibmpc\BIOS_IBM5150_24APR81_5700051_U33.BIN`
IBM 5150 U33	19 Oct 1981	8K	0xFE000	`machines\ibmpc\BIOS_IBM5150_19OCT81_5700671_U33.BIN`
IBM 5150 U33	16 AUG 1982	8K	0xFE000	`machines\ibmpc82\BIOS_5150_16AUG82_5000024_U33.BIN`
IBM 5150 U33	27 Oct 1982	8K	0xFE000	`machines\ibmpc82\BIOS_5150_27OCT82_1501476_U33.BIN`

BASIC ROMS

Basic version C1.0 ROM

Description	Size	Address	Location
BASIC C1.0 U29	8K	0xF6000	`machines\ibmpc\IBM 5150 - Cassette BASIC version C1.00 - U29 - 5700019.bin`
BASIC C1.0 U30	8K	0xF8000	`machines\ibmpc\IBM 5150 - Cassette BASIC version C1.00 - U30 - 5700027.bin`
BASIC C1.0 U31	8K	0xFA000	`machines\ibmpc\IBM 5150 - Cassette BASIC version C1.00 - U31 - 5700035.bin`
BASIC C1.0 U32	8K	0xFC000	`machines\ibmpc\IBM 5150 - Cassette BASIC version C1.00 - U32 - 5700043.bin`
BASIC C1.0	32K	0xF6000	`machines\ibmpc\ibm-basic-1.00.rom`

Basic version C1.1 ROM

Description	Size	Address	Location
BASIC C1.1 U29	8K	0xF6000	`machines\ibmpc82\IBM 5150 - Cassette BASIC version C1.10 - U29 - 5000019.bin`
BASIC C1.1 U30	8K	0xF8000	`machines\ibmpc82\IBM 5150 - Cassette BASIC version C1.10 - U30 - 5000021.bin`
BASIC C1.1 U31	8K	0xFA000	`machines\ibmpc82\IBM 5150 - Cassette BASIC version C1.10 - U31 - 5000022.bin`
BASIC C1.1 U32	8K	0xFC000	`machines\ibmpc82\IBM 5150 - Cassette BASIC version C1.10 - U32 - 5000023.bin`
BASIC C1.1	32K	0xF6000	`machines\ibmpc82\ibm-basic-1.10.rom`

Launching

Make sure these files are next to ibm_pc.exe:

Bm437_IBM_CGA.FON
Bm437_IBM_MDA.FON

Command-Line:

Switch	Switch (ALT)	Description	Values
`-config <config_file>`	`-c <config_file>`	Set the config file	file path
`-o <offset>`	N/A	Set the memory offset for the next ROM file.	`0x00000` - `0xFFFFF`
`<rom_file>`	N/A	Path to a ROM file. It is loaded at the current offset.	file path
`<A-D>: <disk_path>`	N/A	Load a disk image into a drive.	`A`, `B`, `C`, `D` ; file path
`-disk-write-protect`	`-dwp`	Write protect the next loaded disk.	N/A
`-disks <0-4>`	`-ds <0-4>`	Number of floppy drives present. 0-4.	`0` - `4`
`-video <video_adapter>`	`-v`	Selects which display adapter to emulate	`MDA`, `CGA`
`-ram <ram>`	`-r <ram>`	Amount of conventional RAM.	16KB - 736KB
`-sw1 <sw1>`	N/A	Value of motherboard DIP switch SW1	`0` - `255`
`-sw2 <sw2>`	N/A	Value of motherboard DIP switch SW2	`0` - `255`
`-model <model>`	N/A	Motherboard model	`5150_16_64`, `5150_64_256`
`-dbg`	N/A	Enables the debug UI	N/A

Notes

Numbers can be written in decimal, hexadecimal (0x), or binary (0b) form.
RAM can be provided in KB or BYTES.
When a ROM is loaded, -o is automatically incremented by the files size; You can chain ROM files with a single -o <offset>
If a DIP switch (sw1, sw2) isnt provided; it is set automatically based on the provided config

Example:

ibm_pc.exe -o 0xF6000 cb10_1.bin cb10_2.bin cb10_3.bin cb10_4.bin bios.bin -video CGA -ram 640 -model 5150_64_256 A: msdos4_startup.img

Means:
 Load cb10_1.bin (2K file) at 0xF6000
 Load cb10_2.bin (2K file) at 0xF8000
 Load cb10_3.bin (2K file) at 0xFA000
 Load cb10_4.bin (2K file) at 0xFC000
 Load bios.bin   (8K file) at 0xFE000
 Video adapter is a CGA Card
 640KB conventional RAM installed
 Model 64KB-256KB Motherboard
 msdos4_startup.img disk is in drive A:

Configuration File:

The emulator supports configuration files written in a custom structured INI-like format called TOMI (Tom’s Object Markup INI).
It extends traditional INI syntax with support for inline structures and nested data, making it easy to define complex machine setups.

Format:

Basic Key-Value Pairs

Each setting is defined as a key-value pair.
The assignment character = associates a key with a value. Whitespace is optional.

  key1=value
  key2 = value
  key3 = 'value'
  key4 = "value"
  ...

Multiple pairs can also appear on the same line, separated by commas:

  key1=value, key2 = value, key3 = 'value', key4 = "value", ...

Structs

A struct is a collection of key-value pairs grouped together using square brackets [ ]. This allows related settings to be logically grouped.

  struct = [
    key1=value,
    key2 = value,
    key3 = 'value',
    key4 = "value",
    ...
  ]

Structs can also be written in a single line:

  struct = [ key1=value, key2 = value, key3 = 'value', key4 = "value", ... ]

Settings:

Key	Type	Description	Values
`model`	ENUM	Motherboard model	`5150_16_64`, `5150_64_256`
`video_adapter`	ENUM	Selects which display adapter to emulate	`MDA`, `CGA`, `CGA40`, `CGA80`
`conventional_ram`	INT	Amount of conventional RAM installed	`16K` - `736K`
`num_floppies`	INT	Number of floppy drives present	`0` - `4`
`sw1`	INT	Value of motherboard DIP switch SW1	`0` - `255`
`sw2`	INT	Value of motherboard DIP switch SW2	`0` - `255`
`sw1_override`	BOOL	Forces manual SW1 value instead of auto-calculated	`true`, `false`
`sw2_override`	BOOL	Forces manual SW2 value instead of auto-calculated	`true`, `false`
`disk`	STRUCT	Defines one or more floppy disk drives	See below
`rom`	STRUCT	Defines one or more ROM images	See below
`texture_scale_mode`	ENUM	Texture sampling mode	`Nearest`, `Linear`
`display_scale_mode`	ENUM	Display scaling behavior	`Fit`, `Stretched`
`display_view_mode`	ENUM	Display framing mode	`Cropped`, `Full`
`correct_aspect_ratio`	BOOL	Enables 4:3 aspect correction	`true`, `false`
`emulate_max_scanline`	BOOL		`true`, `false`
`mda_font`	STRING	Path to the MDA font file	file path
`cga_font`	STRING	Path to the CGA font file	file path
`dbg_ui`	BOOL	Enables the debug UI	`true`, `false`

ROM settings:

Key	Type	Description	Values
`path`	STRING	Path to the ROM file	file path
`offset`	INT	The offset to load the ROM file	`0x00000` - `0xFFFFF`

DISK settings:

Key	Type	Description	Values
`path`	STRING	Path to the Disk file	file path
`drive`	INT	The drive to load the disk file in.	`A`, `B`, `C`, `D`
`write_protect`	BOOL	write protects the drive	`true`, `false`

Notes

Each disk or rom struct can appear multiple times to define multiple drives or ROMS.
Numbers can be written in decimal, hexadecimal (0x), or binary (0b) form.
Comments start with ; and extend to the end of the line.
Missing values fall back to defaults defined in the emulator.
If a sw1_override or sw2_override is false; the associated SW is set automatically based on the provided config
RAM must be provided in BYTES.

Example INI:

; ----------------- PC Config ------------------
model = '5150_64_256'         ; 5150_16_64, 5150_64_256
video_adapter = 'CGA'         ; MDA, CGA, CGA40, CGA80
conventional_ram = 0x40000    ; 0x4000 - 0xB8000 (16K - 736K)
num_floppies = 2              ; 0, 1, 2, 4
; ----------------------------------------------

; --------------- DIP SWITCHES -----------------
sw1_override = false
sw2_override = false
sw1 = 0b00000000
sw2 = 0b00000000
; ----------------------------------------------

; --------------- Floppy Drives ----------------
disk = [ drive = 'A', path = 'floppies/msdos4_startup.img'  ]
disk = [ drive = 'B', path = 'floppies/msdos4_working6.img' ]
; ----------------------------------------------

; -------------------- ROMS --------------------
rom = [ address = 0xF6000, path = 'roms/5150cb10_1.bin' ]
rom = [ address = 0xF8000, path = 'roms/5150cb10_2.bin' ]
rom = [ address = 0xFA000, path = 'roms/5150cb10_3.bin' ]
rom = [ address = 0xFC000, path = 'roms/5150cb10_4.bin' ]
rom = [ address = 0xFE000, path = 'roms/BIOS_IBM5150_27OCT82.BIN' ]
rom = [ address = 0xC8000, path = 'roms/expansion_rom.bin' ]
; ----------------------------------------------

; --------------- Display Config ---------------
texture_scale_mode = 'Nearest' ; Nearest, Linear
display_scale_mode = 'Fit'     ; Fit, Stretched
display_view_mode = 'Cropped'  ; Cropped, Full
correct_aspect_ratio = true
emulate_max_scanline = true
; ----------------------------------------------

; --------------- Display Fonts ----------------
mda_font = 'fonts/Bm437_IBM_MDA.FON'
cga_font = 'fonts/Bm437_IBM_CGA.FON'
; ----------------------------------------------

; ------------------- DEBUG --------------------
dbg_ui = false
; ----------------------------------------------

Name		Name	Last commit message	Last commit date
Latest commit History 81 Commits
config		config
fonts		fonts
lib		lib
scripts		scripts
src		src
vc		vc
.gitattributes		.gitattributes
.gitignore		.gitignore
.gitmodules		.gitmodules
Multiple Interrupts.txt		Multiple Interrupts.txt
ports.md		ports.md
readme.md		readme.md
sources.md		sources.md

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IBM PC Emulator

Emulated Hardware

Building

FONT Files

ROM Files

IBM PC 5150 ROM

BASIC ROMS

Basic version C1.0 ROM

Basic version C1.1 ROM

Launching

Command-Line:

Notes

Example:

Configuration File:

Format:

Basic Key-Value Pairs

Structs

Settings:

ROM settings:

DISK settings:

Notes

Example INI:

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tommojphillips/ibm_pc

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IBM PC Emulator

Emulated Hardware

Building

FONT Files

ROM Files

IBM PC 5150 ROM

BASIC ROMS

Basic version C1.0 ROM

Basic version C1.1 ROM

Launching

Command-Line:

Notes

Example:

Configuration File:

Format:

Basic Key-Value Pairs

Structs

Settings:

ROM settings:

DISK settings:

Notes

Example INI:

About

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