Memory managers in DOS HIMEM.SYS manages which type of memory resource on DOS-based systems?

Introduction / Context:
DOS memory is historically segmented into conventional, upper, high, expanded (EMS), and extended (XMS). HIMEM.SYS is a High Memory Manager that enables DOS and applications to utilize memory above the first megabyte via the XMS standard.

Given Data / Assumptions:

• HIMEM.SYS is loaded in CONFIG.SYS.
• We distinguish extended (XMS) from expanded (EMS).
• Other drivers like SMARTDRV.SYS (disk cache) depend on XMS availability.

Concept / Approach:

HIMEM.SYS implements the XMS API, controlling access to extended memory and the High Memory Area (HMA). It allows DOS to move parts of itself “HIGH” (via DOS=HIGH), but the manager itself is responsible for brokering XMS blocks to clients such as disk caches and Windows 3.x.

Step-by-Step Solution:

Verification / Alternative check:

Without HIMEM.SYS, commands referencing XMS (for example, SMARTDRV) either fail or run in reduced capability. Adding HIMEM.SYS restores XMS reporting and usage, confirming its role.

Why Other Options Are Wrong:

a: DOS=HIGH is a CONFIG.SYS directive that leverages HIMEM.SYS; it is not what HIMEM.SYS “controls.”

b: RMDRIVE.SYS is unrelated to XMS management.

c: SMARTDRV.SYS is a disk cache that consumes XMS; it is not the memory manager.

e: Not applicable because Extended Memory is correct.

Common Pitfalls:

Confusing EMS with XMS; assuming EMM386 replaces HIMEM—EMM386 depends on HIMEM to access XMS.

Final Answer:

Extended Memory