Editing DR-DOS (section)

==={{anchor|5.0}}DR&nbsp;DOS 5.0===
DR&nbsp;DOS version 5.0 (code-named "Leopard") was released in May 1990,<ref name="Caldera_1996_Suit"/><!-- or August 1990<ref name="Salemi_1991_DR6"/> --> still reporting itself as "PC&nbsp;DOS 3.31" for compatibility purposes, but internally indicating a single-user BDOS 6.4 kernel. (Version 4 was skipped to avoid being associated with the relatively unpopular [[MS-DOS 4.0]].) This introduced [[ViewMAX]], a [[Graphics Environment Manager|GEM]]-based [[GUI]] file management shell.<ref name="CW_1990_DR5"/><ref name="Rosch_1991_DR5"/> ViewMAX's startup screen would present the slogan "Digital Research - We make computers work".<ref name="Digital_Research_1990_We_Make_Computers_Work"/><ref name="Elliott_2013_ViewMAX1"/><ref name="Elliott_2013_ViewMAX2"/> DR&nbsp;DOS 5.0 also introduced the patented [[BatteryMAX]] power management system, bundled disk-caching software (DRCACHE), a remote file transfer tool (FILELINK), a cursor shape configuration utility (CURSOR), and offered a vastly improved memory management system (MemoryMAX).<ref name="CW_1990_DR5"/><ref name="Rosch_1991_DR5"/> For compatibility purposes, the DR&nbsp;DOS 5.0 system files were now named [[IBMBIO.COM]] (for the DOS-BIOS) and [[IBMDOS.COM]] (for the BDOS kernel) and due to the advanced loader in the boot sector could be physically stored anywhere on disk.<ref name="Rosch_1991_DR5"/> The OEM label in the boot sectors was changed to "IBM␠␠3.3".

[[File:Carry-i-front-and-rear.jpg|thumb|right|250px|Front and rear views of the ''[[Carry-I]]'' book-sized diskless workstation, bundled with DR&nbsp;DOS 5.0, based on an [[Intel 80286]] processor and produced by Taiwan's [[Flytech Technology]] {{Circa|1991}}]]

DR&nbsp;DOS 5.0 was the first DOS to include load-high capabilities. The kernel and data structures such as disk buffers could be [[relocation (computing)|relocate]]d in the [[High Memory Area]] (HMA), the first 64&nbsp;KB of [[extended memory]] which are accessible in [[real mode]]. This freed up the equivalent amount of critical "base" or [[conventional memory]], the first 640&nbsp;KB of the PC's RAM – the area in which all DOS applications run.<ref name="Rosch_1991_DR5"/>

Additionally, on [[Intel 80386]] machines, DR&nbsp;DOS's EMS memory manager allowed the operating system to load DOS device drivers into upper memory blocks, further freeing base memory.

DR&nbsp;DOS 5.0 was the first DOS to integrate such functionality into the base OS (loading device drivers into [[upper memory block]]s was already possible using third-party software like [[QEMM]]). This allowed it, on 286 systems with supported chipsets and on 386 systems, to provide significantly more free conventional memory than any other DOS. Once drivers for a mouse, multimedia hardware and a network stack were loaded, an MS-DOS/PC&nbsp;DOS machine typically might only have had 300 to 400&nbsp;KB of free conventional memory – too little to run much late-1980s software. In contrast to this, DR&nbsp;DOS 5.0, with a little manual tweaking, could load all this and still keep all of its conventional memory free – allowing for some necessary DOS data structures, as much as 620&nbsp;KB out of the 640&nbsp;KB. With MEMMAX&nbsp;+V, the conventional memory region could even be extended into unused portions of the graphics adapter card typically providing another 64 to 96&nbsp;KB more free DOS memory.

Because DR&nbsp;DOS left so much conventional memory available, some old programs using certain address wrapping techniques failed to run properly as they were now loaded unexpectedly (or, under MS-DOS, "impossibly") low in memory – inside the first 64&nbsp;KB segment (known as "[[low memory]]"). Therefore, DR&nbsp;DOS 5.0's new MEMMAX&nbsp;-L command worked around this by pre-allocating a [[chunking (computing)|chunk]] of memory at the start of the memory map in order for programs to load above this barrier (but with less usable conventional memory then). By default, MEMMAX was configured for +L, so that applications could take advantage of the extra memory.