Exercise 1: Why MBR Holds Only Four Primary Partitions — Possible Solution
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Explanation:

Per the chapter's own breakdown of the MBR's 512-byte structure, the
partition table itself occupies exactly 64 bytes -- not "up to" 64
bytes, a fixed 64 bytes, no more and no less, sitting between the 446
bytes of boot code and the final 2-byte boot signature. Within that
fixed 64-byte space, each individual partition entry takes up exactly
16 bytes. 64 bytes divided by 16 bytes per entry gives exactly four
entries -- there is no more room in that fixed structure for a fifth
entry, since the MBR format was defined with this fixed layout from
the start and has no mechanism to grow that 64-byte region larger.
This is a genuine structural limit built into the format itself, not
an arbitrary or configurable restriction.

-- What the extended/logical partition workaround actually does --
--
-- Since a new true PRIMARY partition entry can never be added beyond
-- the fourth, the historical workaround takes a different approach:
-- one of the four available primary slots is designated as an
-- "extended" partition instead of an ordinary data partition. This
-- extended partition doesn't hold data directly -- instead, it acts
-- as a container that itself holds a linked chain of additional
-- "logical" partitions inside it, each one built as its own small
-- data structure referencing the next. This doesn't add more room to
-- the fixed 64-byte primary table itself -- it works around the
-- limit by nesting additional partition information inside one of
-- the four primary slots, rather than genuinely expanding the
-- 4-entry structure.

WHY THIS WORKS AS AN ANSWER
------------------------------
This derives the 4-partition limit directly from the chapter's own
stated byte-level structure (64 bytes / 16 bytes per entry = 4),
rather than just stating "MBR only allows four," and explains the
extended/logical workaround as nesting inside one slot rather than
genuinely expanding the fixed table.