The 486 and modern Pentium style CPUs have 32 address wires, so they can directly address a maximum of 4 Gigabytes of RAM. Unfortunately, even though the PC hardware is capable of addressing these huge amounts of memory, DOS isn't! EXPANDED MEMORY (obsolete, but sometimes the hapless PC technician still comes across it on some old legacy systems) In an attempt to increase the memory used by DOS application programs, the Expanded Memory System (EMS) was introduced by Lotus, Intel and Microsoft. Ultimately it was the key product in Microsoft's growth from a programming languages company to a diverse software development firm, providing the company with essential revenue and marketing resources. It was also the underlying basic operating system on which early versions of Windows ran as. The disadvantages were all too apparent. As well as it's slow performance, application software had to be specifically written for the LIM 4.0 driver software. Memory adapter cards are now a thing of the past as more and more memory is being integrated onto the. Now we have taken a quick look at the system configuration files, s and t, we will summarise the sequence of events from power on to the command processor prompt for an MS-DOS based PC. To go some way to meeting this requirement, Microsoft added drivers and memory management utilities to MS-DOS-5, and onwards, to support Extended Memory. This is memory above the 1MB 8086/8088 addressing capability, so it is unsuitable for PC XTs. Exit the editor by typing : alt f then x STEP 4: Now reboot the PC from the A: drive: To do this, leave your disk in the A: drive, and press the RESET button, or hold down the Ctrl and Alt keys and then. Copy s and t from the root directory of drive C: drive to drive A:. Add an extra line into s to enable the EMS driver. Check the memory configuration to confirm the new 1024KB EMS portion. The 1MB address space was divided up for Application programs, the OS, the BIOS ROM and the Video Display, as shown in the memory map below. The bottom 640KB of the address space is known as conventional memory and is used by DOS and DOS. Unfortunately the old DOS 640KB limit still applied to conventional DOS application programs but new programs can be specially written to utilise the vast extended memory area. Microsoft's extended memory manager is known as HIMEM. However, it is wise to become familiar with it, as many DOS machines still have EMS installed. The games fraternity, until quite recently, used EMS to increase the size of DOS based games. This is an upper memory manager and EMS emulator, for use with extended memory. Note: Extended memory is discussed later in this section. As EMS is probably only needed on the odd occasion, e.g., to run DOS based games 5, it is best to make.