ほど～ないNot as ... as
Use ほど～ない to say that A does not reach the degree represented by B: A is not as tall, frequent, difficult, skilled, or otherwise great as B.
Reading the comparison correctly
The noun phrase immediately before ほど is the benchmark. The negative ending then says that A falls short of that benchmark on the relevant scale. It does not mean that A completely lacks the quality.
弟は兄ほど背が高くない。
The younger brother is not as tall as the older brother.
AnalyzeA relative shortfall
この町も便利だが、東京ほど便利ではない。
This town is convenient too, but it is not as convenient as Tokyo.
AnalyzeThe town is explicitly described as convenient. The negative ending only places it below Tokyo.
Different kinds of scale
The comparison can concern ability, quantity, frequency, time, importance, difficulty, and many other qualities that can vary by degree.
Leaving out what is already clear
新しいパソコン、使ってみた？
Have you tried the new computer?
Analyzeうん。前の機種ほど重くないし、動作も速いよ。
Yes. It is not as heavy as the previous model, and it runs faster too.
AnalyzeThe new computer is omitted in the reply because it is already the subject of the conversation.
Two items versus an unmatched item
In an ordinary two-item comparison, A and B are identified and the negative ending places A below B. By contrast, the pattern ほど～はない can compare B with an entire implied group and say that nothing else matches it.
More examples
今年の試験は去年の試験ほど難しくなかった。
This year's exam was not as difficult as last year's.
Analyzeケンはミカほど料理が上手ではない。
Ken is not as good at cooking as Mika.
Analyzeこの部屋は隣の部屋ほど広くない。
This room is not as spacious as the room next door.
Analyze最近は以前ほど図書館に行かない。
Recently, I have not been going to the library as often as before.
Analyzeこの会社はあの会社ほど大きくないが、利益は安定している。
This company is not as large as that one, but its profits are stable.
Analyze帰りの電車は朝の電車ほど混んでいなかった。
The train home was not as crowded as the morning train.
Analyze弟は兄ほどたくさん食べない。
The younger brother does not eat as much as the older brother.
Analyze