When such a chip is put in a PC it is read-only because the design of the PROM burner) the input current can be made so high that a bit pattern isįorced into the chip despite its 'read-only' design. Means is that by putting the chip in some piece of special equipment (a Writing into a read-only chip sounds like a contradiction in terms. The bit pattern may in fact be data or a program. A chip with an unchangeable bit pattern burned into it. This is a generic term which appliesĮqually to Conventional Memory, Expansion Memory, Extended Memory, Expanded Some machinesĬonsequently, it takes 2 bytes to hold a Segment part and 2 bytes to holdįinally then, it takes 4 bytes to hold a complete memory address of theġ Mb-1 = 0xFFFF:000F End System BIOS areaĨ96 Kb 0圎000:0000 Start System BIOS areaĨ96 Kb-1 = 0xDFFF:000F End Expansion card BIOS areaħ68 Kb 0xC000:0000 Start Expansion card BIOS area To 0xFFFF can be stored in 2 bytes (1 word on some machines. So all values from 0 to 0xFF can be stored in 1 byte, and all values from 0 Now, in 0 to 255 there are 256ĭifferent values, which is precisely how many different values can be Since 0xFF = 255, then 0 to 0xFF = 0 to 255. ThusĠx0013:0005 is Normalized, whereas the other forms aren't. Part is from 0 to 0xF the address is said to be Normalized. That is, all represent physical address 309. Lo andīehold! The infamous 640 Kb DOS memory limit consists of memory addressesįrom 0 to 655,359, that is, 0 to 0x9FFF:000F.Īnother example: 1 Mb of memory occupies addresses from 0 to 0xFFFF:000F.

What does this number really mean? Well, the Segment and Offset parts areĪdded by shifting the Segment left one (hex) digit and then adding the The Segment part, and on the right is the Offset part. Just to make things difficult, memory addresses are normally written not as The preceding would suggest 360 Kb floppies hold 360 * 1024 = 368,640 bytesįloppy disk sizes (that is, available space): Other writers use the convention of appending an 'h' or an 'H' to hexġ Mb = 1 Megabyte = 1024 * 1 Kb = 1,048,576 bytes. I shall use theĬonvention of preceding every hex number with 0x. The other way is to specify the number in hexadecimal. One way is to specify the number in decimal, just by stating it. In this article I shall refer to numbers in two ways. The craft of programming is replete (filled to excess) with funny little

PC Memory - A tutorial on PC memory and hex arithmetic CMOS Memory = Complementary Metal-Oxide Semiconductor (read/write) Memory.EPROM = Erasable Programmable Read-Only Memory.Memory - A tutorial on PC memory and hex arithmetic

Hex fiend how to find process memoru