Pure64 v0.5.0 - Manual

Pure64 currently works with the FAT16 file system. This file system was chosen because it is the most compatible between other OS's (Windows, Mac, Linux, etc).
Pure64 loads your software (OS kernel, Demo, etc) to memory address 0x0000000000100000 (The start of the second megabyte of RAM). Once your software is loaded into memory Pure64 will start to run it. At this point Pure64 is done and your software is in full control of the computer.

System Requirements:

A computer with a 64-bit compatible CPU

A FAT16 formatted hard drive

At least 2 MiB of RAM

How to load Pure64:

An example boot sector is available with Pure64. The only requirement is that Pure64 is loaded to 32-bit memory address 0x00008000.

Memory Map:

This memory map shows how physical memory looks after Pure64 is finished.

Start Address	End Address	Size	Description
0x0000000000000000	0x0000000000000FFF	4 KiB	IDT - 256 descriptors (each descriptor is 16 bytes)
0x0000000000001000	0x0000000000001FFF	4 KiB	GDT - 256 descriptors (each descriptor is 16 bytes)
0x0000000000002000	0x0000000000002FFF	4 KiB	PML4 - 512 entries, first entry points to PDP at 0x3000
0x0000000000003000	0x0000000000003FFF	4 KiB	PDP - 512 enties
0x0000000000004000	0x0000000000007FFF	16 KiB	Pure64 Data
0x0000000000008000	0x000000000000FFFF	32 KiB	Pure64 - After the OS is loaded and running this memory is free again
0x0000000000010000	0x000000000004FFFF	256 KiB	PD - Room to map 64 GiB
0x0000000000050000	0x000000000009FFFF	320 KiB	Free
0x00000000000A0000	0x00000000000FFFFF	384 KiB	ROM Area
			VGA mem at 0xA0000 (128 KiB) Color text starts at 0xB8000
			Video BIOS at 0xC0000 (64 KiB)
			Motherboard BIOS at F0000 (64 KiB)
0x0000000000100000	0xFFFFFFFFFFFFFFFF	1+ MiB	Your software is loaded here

When creating your Operating System or Demo you can use the sections marked free, however it is the safest to use memory above 1 MiB.

Information table:

Pure64 stores an information table in memory that contains various pieces of data about the computer before it passes control over to the software you want it to load. The Pure64 information table is located at 0x0000000000005000 and ends at 0x00000000000057FF (2048 bytes).

Memory Address	Variable Size	Name	Description
0x5000	64-bit	ACPI	Address of the ACPI tables
0x5008	32-bit	BSP_ID	APIC ID of the BSP
0x5010	16-bit	CPUSPEED	Speed of the CPUs in MegaHertz (MHz)
0x5012	16-bit	CORES_ACTIVE	The number of CPU cores that were activated in the system
0x5014	16-bit	CORES_DETECT	The number of CPU cores that were detected in the system
0x5016 - 0x501F			For future use
0x5020	16-bit	RAMAMOUNT	Amount of system RAM in Mebibytes (MiB)
0x5022 - 0x502F			For future use
0x5030	8-bit	MBR	MBR Boot Flag. Set to 1 if the disk uses MBR, 0 if not
0x5031	8-bit	IOAPIC_COUNT	Number of IO-APICs in the system
0x5032 - 0x503F			For future use
0x5040	32-bit	VIDEOBASE	Base memory address for video display, 0 if not configured
0x5044	16-bit	VIDEOX	Video display width in Pixels
0x5046	16-bit	VIDEOY	Video display height in Pixels
0x5048 - 0x505F			For future use
0x5060	64-bit	LAPIC	Local APIC address
0x5068...	64-bit	IOAPIC	IO-APIC addresses (based on IOAPIC_COUNT)
0x5100...	8-bit	APIC_ID	APIC ID's for valid CPU cores (based on CORES_ACTIVE)

A copy of the E820 System Memory Map is stored at memory address 0x0000000000004000. Each E820 record is 24 bytes in length and the memory map is terminated by a blank record.

Variable	Variable Size	Description
Starting Address	64-bit	The starting address for this record
Length	64-bit	The length of memory for this record
Memory Type	32-bit	Type 1 is usable memory, Type 2 is not usable

For more information on the E820 Memory Map: OSDev wiki on E820

A copy of the VESA SuperVGA Mode Information is stored at memory address 0x0000000000005C00. A description of what is stored in the structure is available here.